One of the planes was still on fire when the fire departments arrived.

Federal Aviation Administration spokesman Ian Gregor tells New Times another pilot witnessed the midair collision, which occurred around 10 a.m., about 15 miles west-northwest of the Deer Valley Airport.

Names of the people killed in the crash haven't been released at this point.

Gregor adds that the National Transportation Safety Board, which will lead the accident investigation, typically doesn't determine the probable cause of accidents for several months. Even a preliminary report takes a week or two, he says.